Micro light emitting diode display panel and driving method thereof

ABSTRACT

A micro light emitting diode display panel including a plurality of pixels and a control element is provided. One of the pixels include a first sub-pixel. The first sub-pixel includes two micro light emitting diodes having different light wavelengths and controlled independently. The control element controls driving currents to the two micro light emitting diodes according to a gray level of the first sub-pixel, wherein a ratio of the driving current of the micro light emitting diode with larger light wavelength to the driving current of the micro light emitting diode with smaller light wavelength increases as the gray level of the first sub-pixel increases. A driving method of the micro light emitting diode display panel is also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan applicationserial no. 106130555, filed on Sep. 7, 2017. The entirety of theabove-mentioned patent application is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION Field of the Invention

The invention is related to a display panel and a driving methodthereof, and particularly to a micro light emitting diode display paneland a driving method thereof.

Description of Related Art

Along with evolution of photoelectric technologies, the solid-statelighting (e.g., the light emitting diode) has been widely used invarious fields such as road illumination, large outdoor board, trafficsignals and so on. Recently, a micro light emitting diode display panelhas been further developed which uses micro light emitting diodes withdifferent colors as sub-pixels in the display panel.

In high-resolution or large-size micro light emitting diode displaypanels, the circuit is easily damaged by heat due to high drivingcurrent density. In addition, when using small current to drive themicro light emitting diode, the light wavelength of the micro lightemitting diode becomes shorter as the driving current density isincreased and the display image may be get worse under the impact ofcolor shift.

FIG. 1 is a relationship diagram of a current density and a wavelengthof a micro light emitting diode. Taking a green micro light emittingdiode as an example, as shown in FIG. 1, when using small current (e.g.,with current density less than 5 A/cm²) to drive the green micro lightemitting diode, the wavelength of the green micro light emitting diodebecomes smaller as the driving current increases; as a result, the greenlight output by the green micro light emitting diode becomes bluer asthe gray level increases (current density increases), and the wavelengthof the green light cannot be consistent under different gray levels.Therefore, it is an issue for persons skilled in the art to find out howto improve the color shift problem caused by change of current density.

SUMMARY OF THE INVENTION

The invention provides a micro light emitting diode display panel and adriving method thereof, which are capable of improving color shiftproblem caused by change of current density.

In the invention, a micro light emitting diode display panel includes aplurality of pixels and a control element. One of the pixels include afirst sub-pixel. The first sub-pixel includes two micro light emittingdiodes having different light wavelengths and controlled independently.The control element controls driving currents to the two micro lightemitting diodes according to a gray level of the first sub-pixel,wherein a ratio of the driving current of the micro light emitting diodewith larger light wavelength to the driving current of the micro lightemitting diode with smaller light wavelength increases as the gray levelof the first sub-pixel increases.

In an embodiment of the invention, a light wavelength difference betweenthe two micro light emitting diodes ranges from 1 nm to 10 nm.

In an embodiment of the invention, current densities of the two microlight emitting diodes are smaller than 3 A/cm² respectively.

In an embodiment of the invention, only the micro light emitting diodewith smaller light wavelength of the first sub-pixel emits light whenthe first sub-pixel is in minimum gray level, and only the micro lightemitting diode with larger light wavelength of the first sub-pixel emitslight when the first sub-pixel is in maximum gray level.

In an embodiment of the invention, the first sub-pixel is a greensub-pixel, and the two micro light emitting diodes are green micro lightemitting diodes.

In an embodiment of the invention, the one of the pixels furthercomprises a second sub-pixel and a third sub-pixel, and the firstsub-pixel, the second sub-pixel and the third sub-pixel are withdifferent colors.

In an embodiment of the invention, the third sub-pixel only comprisesone micro light emitting diode, and the second sub-pixel comprises twomicro light emitting diodes having different light wavelengths andcontrolled independently. The control element controls driving currentsto the two micro light emitting diodes of the second sub-pixel accordingto a gray level of the second sub-pixel, wherein a ratio of the drivingcurrent of the micro light emitting diode with larger light wavelengthto the driving current of the micro light emitting diode with smallerlight wavelength increases as the gray level of the second sub-pixelincreases.

In an embodiment of the invention, the first sub-pixel, the secondsub-pixel and the third sub-pixel are respectively a green sub-pixel, ared sub-pixel and a blue sub-pixel. The red sub-pixel comprises two redmicro light emitting diodes controlled independently and with differentlight wavelengths. The control element controls driving currents to thetwo red micro light emitting diodes according to a gray level of the redsub-pixel, wherein a ratio of the driving current of the red micro lightemitting diode with larger light wavelength to the driving current ofthe red micro light emitting diode with smaller light wavelengthincreases as the gray level of the red sub-pixel increases, the bluesub-pixel comprises two blue micro light emitting diodes controlledindependently and with different light wavelengths, the control elementcontrols driving currents to the two blue micro light emitting diodesaccording to a gray level of the blue sub-pixel, wherein a ratio of thedriving current of the blue micro light emitting diode with larger lightwavelength to the driving current of the blue micro light emitting diodewith smaller light wavelength increases as the gray level of the bluesub-pixel increases.

In the invention, a driving method of a micro light emitting diodedisplay panel includes steps as follow. First of all, a micro lightemitting diode display panel is provided, which has a plurality ofpixels and at least one control element electrically connected to theplurality of pixels, wherein one of the plurality of pixels include afirst sub-pixel. The first sub-pixel includes two micro light emittingdiodes controlled independently and with different light wavelengths.Secondly, the control element respectively controls driving currents tothe two micro light emitting diodes according to a gray level of thefirst sub-pixel, wherein a ratio of the driving current of the microlight emitting diode with larger light wavelength to the driving currentof the micro light emitting diode with smaller light wavelengthincreases as the gray level of the first sub-pixel increases.

In an embodiment of the invention, the driving current of the microlight emitting diode with larger light wavelength is I2, and the drivingcurrent of the micro light emitting diode with smaller light wavelengthis I1. A ratio of I1 to I2 satisfies the equation I1/I2=(W2−W)/(W−W1),wherein W is a target peak wavelength of the first sub-pixel, W1 and W2are peak wavelengths of the two micro light emitting diodes respectivelywhen the two micro light emitting diodes are driven by I1 and I2, andW1<W2.

In an embodiment of the invention, current densities of the two microlight emitting diodes are smaller than 3 A/cm² respectively.

In summary, according to the invention, in the micro light emittingdiode display panel and the driving method thereof, the first sub-pixelhas two micro light emitting diodes with different light wavelengths,and the ratio of the driving currents of the two micro light emittingdiodes changes along with the gray level, such that the consistency ofthe dominant wavelength and light intensity can be maintained underdifferent gray levels. Accordingly, the micro light emitting diodedisplay panel and the driving method thereof are capable of improvingcolor shift problem caused by change of current density in the microlight emitting diodes.

In order to make the aforementioned features and advantages of thedisclosure more comprehensible, embodiments accompanying figures aredescribed in detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a relationship diagram of a current density and a wavelengthof a micro light emitting diode.

FIG. 2 is a partial top view of a micro light emitting diode displaypanel according to a first embodiment of the invention.

FIG. 3 is a schematic view of a wavelength and light intensity of twomicro light emitting diodes in a first sub-pixel of FIG. 2.

FIG. 4 and FIG. 5 are respectively partial top views of micro lightemitting diode display panels in a second embodiment and a thirdembodiment of the invention.

DESCRIPTION OF EMBODIMENTS

FIG. 2 is a partial top view of a micro light emitting diode displaypanel according to a first embodiment of the invention. Referring toFIG. 2, a micro light emitting diode display panel 100 in the firstembodiment of the invention includes a plurality of pixels U and acontrol element 120.

Each pixel U at least include a first sub-pixel 112. The first sub-pixel112 includes a micro light emitting diode 112A and a micro lightemitting diode 112B. The micro light emitting diode 112A and the microlight emitting diode 112B may have the same size so as to facilitatebonding process, which should not be construed as a limitation to theinvention.

The micro light emitting diode 112A and the micro light emitting diode112B are electrically independent of each other and have different lightwavelengths. Here, the light wavelength refers to a wavelengthcorresponding to a maximum light intensity in a spectrum of the microlight emitting diode. FIG. 3 is a schematic view of a wavelength andlight intensity of two micro light emitting diodes 112A and 112B in thefirst sub-pixel 112 of FIG. 2 at a target gray level. Referring to FIG.2 and FIG. 3, a spectrum of the micro light emitting diode 112B and aspectrum of the micro light emitting diode 112A are partiallyoverlapped, and a light wavelength W112B of the micro light emittingdiode 112B is larger than a light wavelength W112A of the micro lightemitting diode 112A. In an embodiment, a difference of the lightwavelength W112A of the micro light emitting diode 112A and the lightwavelength W112B of the micro light emitting diode 112B ranges from 1 nmto 10 nm, and preferably ranges from 3 nm to 5 nm.

The control element 120 is electrically connected to the micro lightemitting diode 112A and the micro light emitting diode 112B in the firstsub-pixel 112, so as to control driving currents to the micro lightemitting diode 112A and the micro light emitting diode 112B according toa gray level of the first sub-pixel 112. In the first embodiment, thecontrol element 120 is disposed on one side of the plurality of pixelsU, and the control element 120 controls the driving current to each ofthe pixels U through connected wires (not shown). In other embodiments,a plurality of control elements 120 may be correspondingly disposedamong the pixels U.

In the first sub-pixel 112, the ratio of the driving current of themicro light emitting diode 112B with larger light wavelength to thedriving current of the micro light emitting diode 112A with smallerwavelength increases as the gray level of the first sub-pixel 112increases.

Specifically, the driving method of the sub-pixel of the micro lightemitting diode display panel 100 satisfies equation 1:I1*(ΔW2/ΔW)+I2*(ΔW1/ΔW)=I  Equation 1wherein ΔW2=W2−W, ΔW1=W−W1, and ΔW=W2−W1.The symbols used in the above relationship equation represents thefollowing:W: target peak wavelength (λ_(p));I1 and I2: driving currents of the micro light emitting diode 112A andthe micro light emitting diode 112B;I: current required when the first sub-pixel 112 is at the target graylevel, wherein I1+I2 is equal to or close to I; andW1 and W2: peak wavelengths (λ_(p)) of the micro light emitting diode112A and micro light emitting diode 112B.In addition, a ratio of I1 to I2 satisfies I1/I2=(W2−W)/(W−W1).Alternately, in another embodiment, W can be the target dominatewavelength (or target centroid wavelength), while W1 and W2 arerespectively dominate wavelengths (or centroid wavelengths) of the microlight emitting diode 112A and micro light emitting diode 112B.

According to FIG. 1, the larger the current density of the micro lightemitting diode, the wavelength shifts to the smaller wavelength. Inother words, when the gray level of the pixel becomes higher, thewavelength of the light beam emitted by the micro light emitting diodebecomes smaller. Therefore, in the first sub-pixel 112 of theembodiment, the driving current ratio of the micro light emitting diode112A with smaller light wavelength and the micro light emitting diode112B with larger light wavelength decreases as the gray level increases.At low gray level, the dominant wavelength of the light emitted by thefirst sub-pixel 112 is mainly dominated by the micro light emittingdiode 112A with smaller light wavelength. As the gray level increases,the dominant wavelength of the light emitted by the first sub-pixel 112may be increased by increasing the current density of the micro lightemitting diode 112B with larger light wavelength. At high gray level,the light wavelength of the light emitted by the first sub-pixel 112 ismainly dominated by the micro light emitting diode 112B with largerlight wavelength, and the light wavelength of the light emitted by thefirst sub-pixel 112 may be adjusted by the micro light emitting diode112A with smaller light wavelength. In an embodiment, only the microlight emitting diode 112A with smaller light wavelength of the firstsub-pixel 112 emits light when the first sub-pixel 112 is in minimumgray level (darkest). In addition, only the micro light emitting diode112B with larger light wavelength of the first sub-pixel 112 emits lightwhen the first sub-pixel 112 is in maximum gray level (brightest).

Because of disposing two micro light emitting diodes with differentwavelength in one of the first sub-pixel 112, the dominant wavelengthcan be controlled by changing the driving current ratio between the twomicro light emitting diodes with different light wavelengths accordingto the gray level, and the current density of each of the micro lightemitting diodes can be reduced. Since the smaller the change of thecurrent density, the smaller the shifting of the light wavelength (asshown in FIG. 1), the color shift of each of the first sub-pixel 112 canbe improved by substituting a single micro light emitting diode with theplurality of micro light emitting diodes with different lightwavelengths. In this manner, the consistency of the light wavelength andthe light intensity can be maintained under different gray level. In anembodiment, the current densities of the two micro light emitting diodes112A and 112B are smaller than 3 A/cm² respectively, thereby improvingthe color shift problem.

In the micro light emitting diode display panel 100, each of the pixelsU further include a second sub-pixel 114 and a third sub-pixel 116. Thefirst sub-pixel 112, the second sub-pixel 114 and the third sub-pixel116 are sub-pixels 110 with different colors (such as red sub-pixel,green sub-pixel and blue sub-pixel). In this manner, the micro lightemitting diode display panel 100 may display images in full-color.

The plurality of pixel U arranged in array to show image (FIG. 2 merelyschematically illustrates four pixels U). In addition, although FIG. 2simply illustrates four display units U electrically connected to onecontrol element 120, what is shown in FIG. 2 should not be construed asa limitation to the invention. In another embodiment, one pixel U orthousands of pixels U may be connected to one control element 120.

The control element 120 controls the status (light emission,non-emission of light or light emission intensity) of each sub-pixel110. For example, the control element 120 may be a microchip, and thecontrol element 120 and the micro light emitting diodes are bonded on asubstrate 13. The substrate 130 may be a printed circuit board (PCB), aflexible printed circuit board (FPCB), a glass plate having wirings or aceramic substrate having wirings.

In the embodiment, there is only one micro light emitting diode (e.g.,micro light emitting diode 114A) in the second sub-pixel 114, and thereis only one micro light emitting diode (e.g., micro light emitting diode116A) in the third sub-pixel 116. The control element 120 is furtherelectrically connected to the micro light emitting diode 114A in thesecond sub-pixel 114 and the micro light emitting diode 116A in thethird sub-pixel 116 so as to control the emission status of the microlight emitting diode 114A and the micro light emitting diode 116A.

For example, the first sub-pixel 112, the second 114 and the thirdsub-pixel 116 may be the green sub-pixel, the red sub-pixel and the bluesub-pixel respectively. In other words, the micro light emitting diode112A and the micro light emitting diode 112B are green micro lightemitting diodes, the micro light emitting diode 114A is a red microlight emitting diode, and the micro light emitting diode 116A is a bluemicro light emitting diode. Among the red light, the green light and theblue light, since human eyes are most sensitive to the green light(looks brighter under the same brightness), the color shift problem(blue shift) is significantly noticed for the green micro light emittingdiode. In the embodiment, by configuring two green micro light emittingdiodes with different light wavelengths in the green sub-pixel, and theratio of the driving current of the two green micro light emittingdiodes changes along with the gray level, the consistency of the lightwavelength and the light intensity of the green light under differentgray levels can be maintained, and therefore the micro light emittingdiode display panel 100 can have good display quality. In anotherembodiment, the first sub-pixel 112, the second sub-pixel 114 and thethird sub-pixel 116 may be a blue sub-pixel, a green sub-pixel and a redsub-pixel respectively, or a red sub-pixel, a green sub-pixel and a bluesub-pixel respectively.

Although the first embodiment discloses that the above method forimproving color shift (by disposing two micro light emitting diodes withdifferent light wavelengths in at least one sub-pixel of each pixel, andthe ratio of the driving current of the two micro light emitting diodeschanges along with gray level) is only applied in one color of sub-pixel(first sub-pixel 112), which should not be construed as limitation tothe invention. In another embodiment, the method for improving colorshift may also be applied in the second sub-pixel 114 and the thirdsub-pixel 116.

FIG. 4 and FIG. 5 are respectively partial top views of micro lightemitting diode display panels in a second embodiment and a thirdembodiment of the invention. Specifically, FIG. 4 and FIG. 5respectively omit illustration of the substrate and only schematicallyshows one pixel U. Referring to FIG. 4, a micro light emitting diodedisplay panel 200 in FIG. 4 is similar to the micro light emitting diodedisplay panel 100 in FIG. 2, wherein the same elements are denoted bythe same reference numerals, and no repetition is incorporated herein.The major difference between the two is that the second sub-pixel 114has two micro light emitting diodes 114A and 114B with different lightwavelengths in the micro light emitting diode display panel 200 forimproving color shift.

Specifically, in the micro light emitting diode display panel 200, thesecond sub-pixel 114 (e.g., red sub-pixel) includes the micro lightemitting diode 114A and the micro light emitting diode 114B. The microlight emitting diode 114A and the micro light emitting diode 114B mayhave the same size so as to facilitate bonding process, which should notbe construed as a limitation to the invention.

In the embodiment, the micro light emitting diode 114A and the microlight emitting diode 114B are red micro light emitting diodes. The twored micro light emitting diodes are electrically independent of eachother and have different light wavelengths. The control element 120 iselectrically connected to the micro light emitting diode 114A and themicro light emitting diode 114B so as to control driving currents todrive the two red micro light emitting diodes (micro light emittingdiode 114A and micro light emitting diode 114B) according to a graylevel of the second sub-pixel 114 (red sub-pixel), wherein a ratio ofthe driving current of the red micro light emitting diode 114A withlarger light wavelength to the driving current of the red micro lightemitting diode 114B with smaller light wavelength increases as the graylevel of the second sub-pixel increases.

Referring to FIG. 5, a micro light emitting diode display panel 300 inFIG. 5 is similar to the micro light emitting diode display panel 200 inFIG. 4, wherein the same elements are denoted by the same referencenumerals, and no repetition is incorporated herein. The major differencebetween the two is that the third sub-pixel 116 has two micro lightemitting diodes 116A and 116B with different light wavelengths in themicro light emitting diode display panel 300 for improving color shift.

Specifically, in the micro light emitting diode display panel 300, thethird sub-pixel 116 (e.g., blue sub-pixel) includes the micro lightemitting diode 116A and the micro light emitting diode 116B. The microlight emitting diode 116A and the micro light emitting diode 116B mayhave the same size so as to facilitate the bonding process, which shouldnot be construed as a limitation to the invention.

In the embodiment, the micro light emitting diode 116A and the microlight emitting diode 116B are blue micro light emitting diodes. The twoblue micro light emitting diodes 116A and 116B are electricallyindependent of each other and controlled respectively. The micro lightemitting diode 116A and the micro light emitting diode 116B havedifferent light wavelengths in a same driving current, for example, thelight wavelength of the micro light emitting diode 116A is larger thanthat of the micro light emitting diode 116B. The control element 120 iselectrically connected to the micro light emitting diode 116A and themicro light emitting diode 116B so as to control driving currents to thetwo blue micro light emitting diodes (micro light emitting diode 116Aand micro light emitting diode 116B) according to a gray level of thethird sub-pixel 116 (blue sub-pixel), wherein a ratio of the drivingcurrent in the blue micro light emitting diode 116A to the drivingcurrent in the blue micro light emitting diode 116B increases as thegray level of the third sub-pixel 116 increases.

In summary, in the micro light emitting diode display panel of theinvention, at least one sub-pixel has two micro light emitting diodeswith different light wavelengths (but have the same color), and theratio of the driving currents of the two micro light emitting diodeschanges along with the gray level, such that the consistency of thedominant wavelength can be maintained under different gray levels. Inthis manner, the micro light emitting diode display panel can improvethe color shift problem due to current density change of the micro lightemitting diodes. In an embodiment, the above-mentioned method forimproving color shift may also be applied to at least one of the secondsub-pixel and the third sub-pixel. In addition, in each of the pixels,the arrangement of the sub-pixels with different colors, the size, andnumber of micro light emitting diode in each of the sub-pixels may varyaccording to requirement and are not limited to the illustration inFIGS. 2, 4 and 5.

Although the invention has been disclosed by the above embodiments, theembodiments are not intended to limit the invention. It will be apparentto those skilled in the art that various modifications and variationscan be made to the structure of the invention without departing from thescope or spirit of the invention. Therefore, the protecting range of theinvention falls in the appended claims.

What is claimed is:
 1. A micro light emitting diode display panel,comprising: a plurality of pixels, wherein one of the pixels comprises afirst sub-pixel that comprises two micro light emitting diodes havingdifferent light wavelengths and controlled independently; and a controlelement, controlling driving currents to the two micro light emittingdiodes according to a gray level of the first sub-pixel, wherein a ratioof the driving current of the micro light emitting diode with largerlight wavelength to the driving current of the micro light emittingdiode with smaller light wavelength increases as the gray level of thefirst sub-pixel increases.
 2. The micro light emitting diode displaypanel according to claim 1, wherein a light wavelength differencebetween the two micro light emitting diodes ranges from 1 nm to 10 nm.3. The micro light emitting diode display panel according to claim 1,wherein current densities of the two micro light emitting diodes aresmaller than 3 A/cm² respectively.
 4. The micro light emitting diodedisplay panel according to claim 1, wherein only the micro lightemitting diode with smaller light wavelength of the first sub-pixelemits light when the first sub-pixel is in minimum gray level, and onlythe micro light emitting diode with larger light wavelength of the firstsub-pixel emits light when the first sub-pixel is in maximum gray level.5. The micro light emitting diode display panel according to claim 1,wherein the first sub-pixel is a green sub-pixel and the two micro lightemitting diodes are green micro light emitting diodes.
 6. The microlight emitting diode display panel according to claim 1, wherein the oneof the pixels further comprises a second sub-pixel and a thirdsub-pixel, and the first sub-pixel, the second sub-pixel and the thirdsub-pixel are with different colors.
 7. The micro light emitting diodedisplay panel according to claim 6, wherein the third sub-pixel onlycomprises one micro light emitting diode, the second sub-pixel comprisestwo micro light emitting diodes having different light wavelengths andcontrolled independently, and the control element controls drivingcurrents to the two micro light emitting diodes of the second sub-pixelaccording to a gray level of the second sub-pixel, wherein a ratio ofthe driving current of the micro light emitting diode with larger lightwavelength to the driving current of the micro light emitting diode withsmaller light wavelength increases as the gray level of the secondsub-pixel increases.
 8. The micro light emitting diode display panelaccording to claim 6, wherein the first sub-pixel, the second sub-pixeland the third sub-pixel are respectively a green sub-pixel, a redsub-pixel and a blue sub-pixel, the red sub-pixel comprises two redmicro light emitting diodes controlled independently and with differentlight wavelengths, the control element controls driving currents to thetwo red micro light emitting diodes according to a gray level of the redsub-pixel, wherein a ratio of the driving current of the red micro lightemitting diode with larger light wavelength to the driving current ofthe red micro light emitting diode with smaller light wavelengthincreases as the gray level of the red sub-pixel increases, the bluesub-pixel comprises two blue micro light emitting diodes controlledindependently and with different light wavelengths, the control elementcontrols driving currents to the two blue micro light emitting diodesaccording to a gray level of the blue sub-pixel, wherein a ratio of thedriving current of the blue micro light emitting diode with larger lightwavelength to the driving current of the blue micro light emitting diodewith smaller light wavelength increases as the gray level of the bluesub-pixel increases.
 9. A driving method of a micro light emitting diodedisplay panel, comprising: providing a micro light emitting diodedisplay panel, having a plurality of pixels and at least a controlelement electrically connected to the pixels, wherein one of the pixelscomprise a first sub-pixel that comprises two micro light emittingdiodes controlled independently and with different light wavelengths;and controlling driving currents to the two micro light emitting diodesvia the control element according to a gray level of the firstsub-pixel, wherein a ratio of the driving current of the micro lightemitting diode with larger light wavelength to the driving current ofthe micro light emitting diode with smaller light wavelength increasesas the gray level of the first sub-pixel increases.
 10. The drivingmethod of the micro light emitting diode display panel according toclaim 9, wherein the driving current of the micro light emitting diodewith larger light wavelength is I2, the driving current of the microlight emitting diode with smaller wavelength is I1, a ratio of I1 to I2satisfies:I1/I2=(W2−W)/(W−W1); wherein W is a target peak wavelength of the firstsub-pixel, W1 and W2 are peak wavelengths of the two micro lightemitting diodes respectively when the two micro light emitting diodesare driven by I1 and I2, and W1<W2.
 11. The driving method of the microlight emitting diode display panel according to claim 9, wherein currentdensities of the two micro light emitting diodes are smaller than 3A/cm² respectively.